Nature lovers, beware: poison hemlock and wild parsnip currently flourishing in Southern Ohio due to continuous wet conditions can cause serious health issues in humans and other mammals, according to Joe Boggs and Eric Draper of The Ohio State University (OSU) Extension, in the blog, Buckeye Yard and Garden onLine.

Poison hemlock (Conium maculatum) and wild parsnip (Pastinica sativa) are non-native plants and members of the carrot family (Apiaceae).

Considered one of America’s deadliest plants, poison hemlock contains highly toxic compounds, which can cause respiratory failure and death in humans and other mammals, according to Boggs and Draper. Although the root is the plant’s most toxic part, all parts of the plant, including its seeds, should be considered poisonous.

According to Boggs and Draper, poison hemlock’s toxins can induce poisoning if ingested or if the toxins enter the body through the nasal passages or the eyes. The plant does not cause skin rashes or blistering upon contact, they said, however, if the plant is handled, the plant’s sap on the skin can enter the eyes through rubbing or can be ingested by handling food.

The sap of wild parsnip contains naturally-occurring compounds, or phytochemicals, which can destroy epithelial skin cells, Boggs and Draper stated. Epithelial skin cells protect the body from long-wave ultraviolet radiation (LWUVR) present in sunlight, they said. When sap on the skin is exposed to LWUVR, the skin can develop discolorations and burn-like symptoms that may last for several months. Symptoms may not appear for 24 hours after exposure to long-wave ultraviolet radiation and severe blistering may not peak for 48 to 72 hours after exposure to LWUVR.

Since wild parsnip and poison hemlock will often grow together in an area, persons experiencing the ill effects of wild parsnip might mistakenly blame poison hemlock for his or her affliction.

Poison hemlock produces tiny white flowers on stalks that give the cluster of flowers an umbrella-shaped appearance, Boggs and Draper stated. Wild parsnip produces yellow flowers on stalks that give the group of flowers a flat-topped appearance.

Both poison hemlock and wild parsnip are prolific seed producers. “Once the flowers mature, the seeds will still be produced on plants that have been cut down,” according to Boggs and Draper.

Wild parsnip can grow to a height of six feet. Poison hemlock can reach a height of eight to 10 feet.

The roots of Queen Anne’s Lace, or wild carrot, are edible and resemble the roots of poison hemlock, resulting in misidentification and accidental poisonings. The purple stems of poison hemlock should not be misidentified as the purple stems of the edible and medicinal garden angelica (Angelica archangelica), Boggs and Draper warned. People should be careful not to mistake the seeds of poison hemlock for fennel seeds either.

“It’s becoming too late to effectively manage either of these weeds in southern Ohio, but there still may be time to reduce infestations in the central and north part of the state,” according to Draper and Boggs. “While it may be too late for control, it’s not too late to suffer from the toxicity of these plants. They will remain a risk until collapsing later this season.”

To see more photos of these deadly plants and read more information about this topic, check out Boggs’ and Draper’s blog online at https://bygl.osu.edu/node/1321

Joe Boggs is assistant professor for OSU Extension/OSU Entomology. Erik Draper is with OSU Extension, Geauga County, Ohio.

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